Hazardous and radioactive liquid waste disposal method

ABSTRACT

An improved method of disposing of radioactive or hazardous liquids comprises placing the liquids in a container and adding a sodium montmorillonite over intervals until the composition is substantially solid in the container.

This is a continuation of co-pending application Ser. No. 06/743,057,filed on Jun. 10, 1985 (abandoned).

BACKGROUND OF THE INVENTION

The disposal of hazardous and radioactive waste materials is of extremeimportance. Federal and state laws and requirements covering suchdisposals are particularly severe and stringent due to the dangers toplant and animal life if the desired standards are not met and thehazardous or radioactive materials become exposed to the environment.Because of the potential dangers, the U.S. Nuclear Regulatory Commissionhas not only identified the hazardous and radioactive materials to date,which list is continually being amended and updated, but has set forthspecific standards and requirements for protecting the environmentagainst such waste materials. The resulting laws and regulations are setforth in 10 CFR, particularly sections 1-199. Other regulations relatingto transportation, packaging, labeling and identifying hazardous andradioactive materials are also found in 40 CFR 1-799 and 49 CFR 100-177.Other publications which relate to classifying, indexing and discussingradioactive and hazardous waste materials include DOE/LLW-14Tpublication "Waste Classification, A Proposed Methodology ForClassifying Low-Level radioactive Waste", December 1982, DOE/LLW-17T,"Survey Of Chemical And Radiological Indexes Evaluating Toxicity", March1983, FW-874, "Hazardous Waste Land Treatment", April 1983 and FW-872"Guide To The Disposal Of Chemically Stabilized and Solidified Waste",September 1982.

It is the common practice to process liquid hazardous or radioactivematerials by adding absorbents in an attempt to enhance handling andtransportation, as well as eventual storage thereof. The materials thathave been used heretofore include diatomaceous earth, vermiculite orexpanded mica such as zonolite and krolite, portland and gypsum cements,as well as clay materials such calcium bentonites. A problem with suchmaterials is that only a relatively small amount of liquid can beabsorbed or otherwise treated with less than satisfactory results. Forexample, liquid materials are desirably transported and disposed of in55 gallon drums. However, it has been found with the use of theseabsorbents, solid compositions cannot be achieved or if temporarilyachieved, liquid separation occurs during transportation or storage. Anyseparated or free-standing liquids are especially undesirable because ofthe potential danger of leakage from a ruptured or opened container. Itis to the substantial elimination of such problems that the presentinvention is directed.

SUMMARY OF THE INVENTION

An improved method of treating hazardous and radioactive liquid wastematerials comprises placing the materials in a container, such as a 55gallon drum, and slowly adding sodium montmorillonite until the mixturehas substantially solidified. The resulting composition may be handled,transported and stored under a variety of conditions for extendedperiods of time without evidence of liquid separation or deterioration.These and other advantages as well as the specific sodiummontmorillonite compositions used in the invention will be moreparticularly described in the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

The method of solidifying the hazardous and radioactive liquid wastecompositions according to the invention applies to a great variety ofsuch materials. For example, in the radioactive waste disposal field,liquids which must be treated and disposed of include reactor plantliquids such as turbine, cutting and lubricating oils, solvent sludgeswhich are used to degrease the reactor components such as Freon TF,cleaning solvents such as Stoddard solvents, decontamination solvents,and aqueous mixtures of the above-noted hydrocarbon materials,particularly those containing between from 5 to about 75% hydrocarbonsand even up to 100% hydrocarbons. In addition, a great quantity of suchwastes are aqueous liquids, containing over about 95% water contaminatedwith radioactive materials such as greases from reactor plant turbines.Hospital-sourced contaminated liquids contain radioactive materials usedin cancer treatments. From such sources, particularly common materialsinclude the radioactive cobalts such as cobalt 57, cobalt 58 and cobalt60, cesium, plutonium and uranium isotopes, and the like. However, it isto be understood, according to the invention, that any radioactivematerials that are to be disposed of and are defined in the aforesaidlaws, regulations, and documents are intended to be included in thecompositions treated according to the method of this invention, as wellas any later identified and added radioactive materials, regardless ofsource and regardless of the specific radioactive material orradioisotope.

Common hazardous waste materials include acids, bases, chlorinatedhydrocarbons including PCB, dioxins, and the like. Again, these as wellas the radioactive materials may be in substantially aqueous liquids,particularly those having 95% or more water, or they may be aqueousmixtures containing up to substantial amounts of hydrocarbons. Moreover,as used herein, "hydrocarbons" is intended to define any such oil,solvents and other hydrocarbons or non-aqueous liquids as generallydescribed above which have been contaminated with radioactive materialsor which themselves are considered hazardous chemicals according togovernmental regulations.

The material used in the method of the present invention for treatingthe above-described hazardous and radioactive liquid waste materials issodium montmorillonite. As defined herein, sodium montmorillonitecomprises a montmorillonite in which the major exchangeable cation issodium and with smaller amounts of calcium and other exchangeablecations. The preferred materials has over about 50% weightmilliequivalents of sodium and exhibits a number of other properties aswill be discussed hereinafter. A highly useful material is the sodiummontmorillonite naturally occurring in Wyoming and certain areas ofSouth Dakota and Montana which exhibits a unique combination ofcharacteristics which qualify it as an extremely efficient solidifyingagent in treating the waste compositions according to the invention.Because of the large surface area to weight ratio and net negativesurface charge, the concentration of cations, particularly sodium, areheld in an exchangeable position on the montmorillonite particle which,when hydrated, act with the mineral structure to produce ordered waterlayers which are great distances from the particle surfaces. Because ofthis unique characteristic, the sodium montmorillonite, when added to anaqueous liquid results in a non-pourable flexible matrix that does notundergo phase separation except under extreme temperature and/orpressure conditions far beyond those encountered under storage andhandling conditions.

As previously noted, the sodium montmorillonite is that having sodium asthe major exchangeable cation, preferably having over a 50%milliequivalent exchangeable cation concentration, and more preferablybetween about 60 and about 75 sodium meq/%. Other cations includecalcium, commonly between about 20 and about 35 meq/% with other typicalcations including potassium, magnesium, iron, being in the aggregaterange of between about 5 and about 20 meq/%. However, such specificpercentages are to be understood to be in the most preferred material,and materials outside of those specific ranges are to be included,again, so long as the major sodium concentration is present. Of course,the naturally occurring material may be obtained from any source, andsynthetic materials are also to be included within the purview of theinvention.

In addition to the major sodium concentrations, the preferred materialpossesses high colloid content, liquid limits, plate water retention andcation exchange capacity. The colloid content of the sodiummontmorillonite of the invention, is at least about 70%. By the term"colloid content" as used herein, it is intended to define that portionof material that is colloidal in the dispersing medium and has aparticle size less than about 2 microns when it is dispersed. Preferredsodium montmorillonites will exhibit between about 70 and about 75%colloid content according to this definition.

The liquid limit of the sodium montmorillonite is a minimum of about500%. The liquid limit is determined by ANSI/ASTM D-423-66, anddetermines how much water (by weight) the material will hold withoutbecoming liquid. By the term "solid" as used herein, it is intended todefine the compositions which are not pourable. In addition, herein, theterm "substantially solid" is intended to be so defined. Normally upperliquid limits of the sodium montmorillonite material used in theinvention will be about 750%, with nominal averages being about 600%.

Another important feature of the sodium montmorillonite is the amount ofwater adsorption determined by a plate water retention test, thematerial of the invention exhibiting a minimum of about 600%. Thisretention is determined according to ASTM standard E-946, with the upperpractical limit being 1,000% and nominal figures for the most preferredmaterial being between about 750 and about 800%.

The preferred sodium montmorillonite cation exchange capacity is 70meq/100 grms., up to even 95-100 meq/%; nominal ranges of the preferredmaterial are between about 75 and about 80 meq/%.

A desirable moisture content of the material is a maximum of about 10%,by weight, and that can be achieved by simply drying the material priorto adding it to the liquid to be treated. It will be understood thatwhere higher amounts of moisture are present, the effectiveness of thematerial for solidifying the liquid compositions will simply be somewhatreduced.

In treating the liquid, different particle size sodium montmorilloniteshave been found to be more effective depending on the relative water andhydrocarbon content of the liquid. In solidifying liquids having 95% ormore water, the preferred material has at least a major portion ofparticle sizes between about 3/8" and 20 mesh and more preferably atleast a major portion of the particle sizes between 4 and 10 mesh(-4+10). In treating liquid compositions having more than about 5%hydrocarbon, the use of a more finely divided sodium montmorillonite ispreferred. For treating such liquids, at least some and preferably allof the sodium montmorillonite should pass a 200 mesh screen.

The amount of sodium montmorillonite to be used is in a mineral-liquidratio of between about 3:1 and about 1:7, by volume, respectively. Thebulk density of the mineral (sodium montmorillonite) in the -4+10 meshparticle size range is about 70 to about 75 pounds per cubic footwhereas in the 200 mesh range, the density is about 60 to about 63pounds per cubic foot so that, the weight ratio of the mineral-liquidused is also between about 3:1 and about 1:7, by weight, respectively.Within those ranges, it is found that where about 95% or more of theliquid to be treated is water, the amount of mineral used to solidifythe composition is less then that required for liquids containing morehydrocarbons. For example, where about 75% or more of the liquid is ahydrocarbon, such as turbine oil, the amount of mineral used may be upto as high as about 3:1 mineral:liquid. Specifically, in liquidcompositions containing between about 25% and 100% oil, mineral:liquidratios between about 3:1 and about 1:1.6, respectively, were found to besuitable. On the other hand, where the liquid was substantially 100%aqueous, mineral:liquid ratios of between about 1:2 and about 1:5.2 weresuitable. More specifically, when treating liquid waste containing atleast about 95% water, it is preferred to use between about 150 andabout 175 pounds of the -4+10 mesh mineral with between about 45 andabout 48 gallons of liquid in a 55 gallon drum. Preferably when treatingliquids having about 95% or more water, the amount of mineral:liquidratio is between about 1:2 and about 1:7, by weight or volume,respectively. When treating liquids containing 5% or more hydrocarbon,the mineral:liquid ratio is preferably between about 1:2 and about 3:1,respectively.

When adding the montmorillonite, it may be added to the highly aqueouscompositions, without stirring. However, it is not to be added all atonce and instead should be poured into the liquid in portions orfractions, preferably about 1/4 to 1/3 of the total mineral to be used,with at least about 10 minute and preferably 15-20 minute intervalsbetween portion. Thus, for example, between about 40 and about 55 poundsof mineral is added to about 45 to 48 gallons of liquid in a 55 gallondrum. Alternatively, smaller fractions of mineral may be added withshorter intervals. For example, where 25 pound or 1/6 fractions areadded, intervals of a few minutes up to about 10 minutes, and preferablyabout 5 minutes are sufficient. With larger fractions, of say 75 pounds,or one-half of the mineral to be added, longer intervals of 20 minutesand up to 30 minutes are preferred. Where more than about 5% hydrocarbonis present, again, at least a portion or all of the 200 mesh mineral ispreferably used and the mixture is stirred in order to solidify thetotal composition. The method of the invention is preferably used inliquid compositions containing up to 75% hydrocarbon, although, aspreviously noted, it may be used for 100 % hydrocarbon compositions.Where the liquid contains about 5% or more hydrocarbon, the 200 meshmineral may be added rapidly, with stirring and without adding it infractions or between intervals.

Where highly acid or caustic liquids are to be treated it is preferredto neutralize the material to a pH of between about 6.5 and about 9.0prior to treatment with the sodium montmorillonite although the mineralwill be useful for liquids in the pH range from 2-11. Highlyconcentrated acids require proportionately greater amounts of mineral.

For solidifying the liquid compositions according to the invention, itis quite convenient to utilize a 55 gallon open-top drum before treatingand storing the waste liquids. Of course, other containers may also beused, but because of the availability of these 55 gallon drums their useis very desirable. In a specific example of treating liquid according tothe invention, between 45 and 48 gallons of the liquid were poured intothe 55 gallon drum. Fifty pounds of sodium montmorillonite was added tothe drum by pouring the mineral evenly over the liquid surface in orderto cover the entire bottom of the drum with the particulate mineral asevenly as possible. The specific montmorillonite used had a sodiumcontent of between 60 and 75 meq/%, calcium 20-35 meq/%, a colloidcontent of 70-75%, liquid limit of about 600%, a moisture content below10%, a plate water retention of 750-800% and a total cation exchangecapacity of 75-80 meq/100 gm. The liquid contained less than 5%hydrocarbon and the sodium montmorillonite added had a particle size of-4+10 mesh. After 15 to 20 minutes, another 50 pound portion of sodiummontmorillonite was added and evenly distributed, and 15 to 20 minutesthereafter, a third bag was added. After about 30 minutes, the mixturewas inspected and found to be substantially solid. The lid was placed onthe drum and after 24 hours the composition was again inspected andfound to be substantially solid.

Drums containing compositions treated as above-described were subjectedto extremely rough transportation conditions, including beingtransported 1,000 miles to determine if free liquid would becomeseparated. When the transport tests were completed, the drums were cutopen and the solidified mixture was cut in half vertically, and it wasfound that there was no free water in the samples.

In treating the liquid compositions as a further precaution, if there isfree standing liquid on the top of the composition after the appropriateamount of mineral has been added and allowed to stand for 24 hours anadditional 1/2 to 1" of sodium montmorillonite may be added to completethe solidification process, again waiting for 24 hours for inspection.If further free standing liquid occurs, sodium montmorillonite may beused to fill the remaining volume of the drum after which the lid issecured. It has been found that the resulting substantially solidcompositions achieved by following the method described herein areslightly alkaline, inert, non-corrosive, and non-biodegradable inorganicsystems in which the liquid phase as well as the dissolved and suspendedsolids are fixed in a non-pourable flexible matrix that will not exhibitbrittle fragmentation under accidental spill conditions. Unlike priorart adsorbents used heretofore, which concentrate the liquids in porespaces, the sodium montmorillonite of the invention is believed toresult in a physio-chemical bond yielding a stable homogeneous storagecondition which does not undergo phase separation under normaltemperature or pressure conditions as well as such conditions which aresignificantly more extreme than those demonstrated or anticipated inhandling or storing such liquids under existing Federally approvedstorage conditions. Further, there is no evidence to indicate formationof gases or any secondary hazardous products as a result of thesolidification process. These advantages as well as others will beevident to those skilled in the art.

We claim:
 1. An improved method of solidifying a radioactive orhazardous liquid comprising placing said liquid in a container andadding only sodium montmorillonite to said liquid in a ratio of sodiummontmorillonite:liquid of between about 3:1 and 1:7, respectively, untilthe composition comprises an unpourable, free standing solid.
 2. Amethod of solidifying a radioactive or hazardous liquid comprising atleast about 95% water by adding only sodium montmorillonite having amajor portion of particles between about 3/8 inch and 20 mesh thereto ina sodium montmorillonite:liquid ratio of between about 1:2 and about1:7, respectively, in fractions with at least a few minutes intervalbetween fractions, until the composition comprises .[.an unpourable,.]..Iadd.a .Iaddend.free standing solid.
 3. The method of claim 2 whereineach of said fractions is between about 10 and 50% of the total amountadded.
 4. The method of claim 2 wherein each of said fractions isbetween about 1/3 and 1/4 of the total amount added and wherein theintervals between fraction additions is at least about 10 minutes. 5.The method of claim 2 comprising placing between about 40 and 50 gallonsof said liquid in a 55 gallon drum, and adding between about 150 andabout 175 pounds of sodium montmorillonite to said liquid in fractionsof between about 40 and about 55 pounds with at least about 10 minuteintervals between fractions.
 6. A method of solidifying a radioactive orhazardous liquid comprising at least about 5% hydrocarbon by adding onlysodium montmorillonite having a major portion of particles of about 200mesh or smaller thereto in a sodium montmorillonite:liquid ratio ofbetween about 1:2 and 3:1, respectively, with stirring, until thecomposition comprises .[.an unpourable,.]. .Iadd.a .Iaddend.freestanding solid. .Iadd.7. An improved method of solidifying a radioactiveor hazardous liquid comprising adding only sodium montmorillonite tosaid liquid in a ratio of sodium montmorillonite:liquid of between about3:1 and 1:7, respectively, until the composition comprises a freestanding solid. .Iaddend.